Pressure in a pressure vessel of a compressor system may be controlled in various ways. For example, under a load/unload control scheme, a compressor operating at a constant speed is controlled to a load mode or an unload mode in turn. The pressure inside the pressure vessel alternates between a minimum pressure limit and a maximum pressure. Alternatively, a PI control scheme may be used for controlling the compressor. A PI or a PID controller may be used to control a rotational speed of the compressor such that the pressure inside stays at a desired, constant level.
In order to be able to control the pressure inside the pressure vessel, the compressor system may comprise a pressure sensor. Such a sensor may increase the cost of the compressor system. Further, the sensor may be prone to malfunctions and may require regular maintenance.